To maintain an ecological balance within an aquarium, it is necessary to keep the water in the aquarium clean. Cleaning is often accomplished by pumping water from the aquarium to a filter device. The filter device will clean the water by having it pass through a filter medium, and then the cleaned water is returned to the aquarium. Such filtering devices generally include an internal pump driven by an electric motor for pumping the water through the filter medium. Improvements are desirable by increasing the flow rates through the pump, without increasing the impeller size to allow for compact impeller designs.